Food preservative fights cystic fibrosis complication

A common food preservative could one day protect patients with cystic fibrosis against a deadly bacterial infection, a new study suggests.

Experiments in test tubes and in mice have revealed that acidified sodium nitrite - a chemical typically used in the curing of luncheon meat - destroys hardy Pseudomonas aeruginosa microbes. A mutated type of these bacteria, called the "mucoid" form, can contribute to fatal pneumonia in people with the genetic disorder, cystic fibrosis. Doctors can prescribe antibiotics to fight these types of infections, but a number of P. aeruginosa strains show resistance to these drugs.

"Getting mucoid P. aeruginosa is essentially a death sentence for the patient, for the organism can never be eradicated from their lungs," explains Daniel Hassett at the University of Cincinnati College of Medicine in Ohio, US, who led the study.

Cathleen Morrison, chief executive officer of the Canadian Cystic Fibrosis Foundation, agrees that chronic lung infection with the mutated bug is the leading cause of death among CF patients. "P. aeruginosa is the most common virulent respiratory pathogen in cystic fibrosis," she says, adding that over 48% of children and young adults with cystic fibrosis in Canada are infected with the bug.

Strength and weakness

Cystic fibrosis patients produce abnormally viscous mucus in their lungs, which leads to chronic lung damage. The mutated P. aeruginosa makes this worse by making the mucus stickier and harder to clear, which can cause complications. It has a slimy outer layer which gives it some protection from the body's immune system.

But it seems that the very mutation that makes P. aeruginosa much more damaging in CF patients, may also be its weakness.

Hassett and his colleagues were testing whether the mucoid P. aeruginosa could grow using nitrite as a substitute for oxygen - which is depleted in the mucus of CF patients - when they found the nitrate actually killed the microbe.

They then tested the common food agent, used to bind proteins that give meat its characteristic red colour, in mice with P. aeruginosa infection in their lungs. Impressively, a daily 0.5-milligram dose of nitrite killed off the microbes within 16 days.

The researchers believe the mutated form of P. aeruginosa cannot properly dispose of the nitrite metabolically and die as a result.

Toxicity studies

Hassett's team is currently developing a new treatment to battle this infection in humans. "We believe that sodium nitrite could prolong the lives of cystic fibrosis patients for years, if everything goes well."

He has plans to develop a time-release compound in an inhaled form and hopes that clinical trials will be underway within two years.

But Hassett notes that an overdose of nitrites can disrupt oxygen transport. He says that "toxicity studies still need to be performed" but he adds that researchers have used nitrites against cyanide poisoning and to increase blood flow in heart attack patients.

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